This invention relates generally to storage tanks and more particularly to systems for storage tanks designed to prevent overflow both during and subsequent to filling.
It is well known to use storage tanks for holding a variety of fluids such as oil, gasoline, and diesel fuel to name a few. Proper filling of storage tanks is a universal concern, as overfilling of storage tanks may result in spillage, damage to the tank or filling equipment, contamination of land or ground water, or other serious and potentially dangerous results. Concerns over spillage of the tank contents are particularly acute when the tank contents are flammable, toxic and/or environmentally hazardous.
Spillage from fuel tanks on pleasure boats and other marine vessels is particularly troublesome. Some contemporary estimates of such fuel spillage are in excess of six million gallons annually in the United States alone. Globally, fuel spillage is many times this amount. The resultant fuel losses are economically and ecologically detrimental in terms of wasted fuel resources and environmental contamination. The problem has lead the Environmental Protection Agency to mandate that any such spillage be subject to heavy fines.
An internal fuel tank on a marine vessel is typically provided with a vent to enable vapor and fumes to escape under pressure while fuel is being pumped into the fuel tank via the fuel fill tube. As the engine consumes fuel, air is drawn into the tank via the air vent to fill the space from the consumed fuel. Venting is also necessary to accommodate expansion of the fuel when it is heated. During filling of the fuel tank, some fuel may be discharged through the vent into the water as the attendant attempts to fill the tank to capacity. In fact, it is not unknown for filling attendants to purposely fill the tank until fuel is discharged from the vent, using this as an indication that the tank is completely full. It is also possible that fuel may be discharged through the vent subsequent to filling. For example, fuel can be discharged through the vent in a tank filled to capacity as a result of the boat listing from side to side due to waves, wind or other causes. Also, fuel will be discharged through the vent in a tank filled to capacity if a subsequent rise in ambient temperature causes the fuel to expand.
The use of fuel dispensing nozzles that automatically shut off the flow of fuel to the tank when the tank is full can avoid fuel spillage during filling. These nozzles typically operate by sensing a pressure change in the incoming fuel flow that results from filling the tank fill tube. Use of a fuel dispensing nozzle with automatic shut-off will prevent fuel discharge through the fill tube during filling if the fill tube is properly designed to trigger the shut-off at the appropriate time. However, with many designs the automatic shut-off may not be triggered at all because the pressure transition is not sufficient. The result is that fuel will overflow through fill tube if the nozzle is not shut off manually. Because of the location of the vent in many applications, it is also possible that fuel will be discharged through the vent during filling. Discharge through the vent may also occur after filling, even if the automatic shut-off is triggered. For example, if the tank is filled to near capacity, fuel can be discharged through the vent due to boat listing or fuel expansion.
Many prior approaches to spillage rely on the use of a reservoir designed to capture overflow. However, these approaches require additional parts and the use of a reservoir takes up more space on the vessel. None of these approaches address the above-mentioned drawbacks of relying on the automatic shut-off feature of existing fuel dispensing nozzles.
Accordingly, there is a need for a system and method that prevents spillage both during and after filling of a storage tank. It would be desirable to have such a system and method of overflow prevention that facilitates use of automatic shut-off nozzles and does not require provision of an overflow reservoir.
The above-mentioned need is met by the present invention, which provides an overflow prevention system and method for storage tanks that make use of the existing or slightly modified design of the shut-off nozzles that have become accepted in automotive refueling applications. The system includes a flow disturber arranged to travel in the fill tube of the storage tank, a fluid level sensor for sensing fluid level in the storage tank, and an actuator connected between the flow disturber and the fluid level sensor. The actuator causes the flow disturber to move toward the fill tube inlet in response to rising fluid level sensed by the fluid level sensor. The flow disturber is arranged to travel between a first position in which it does not cause the incoming fluid flow to be turbulent and a second position in which it does cause the incoming fluid flow to be turbulent. The flow disturber is provided with a size, shape and texture that will create a transition from laminar to turbulent flow without risking splashback for the operator.
In operation, the actuator is responsive to the fluid level sensor to move the flow disturber to the second position when a predetermined fluid level is reached. The transition from laminar to turbulent flow triggers the automatic shut-off feature of the dispensing nozzle to prevent the tank from being filled beyond the predetermined level.
In one possible embodiment, the fluid level sensor is a float suspended in the storage tank and the actuator is a mechanical linkage, such as a rod or a flexible cable assembly, connecting the float to the flow disturber.
In another possible embodiment, the fluid level sensor is a float suspended in the storage tank and the actuator comprises a pair of fluid cylinders arranged to transfer motion of the float to the flow disturber.
In yet another possible embodiment, the fluid level sensor is disposed inside the storage tank and produces an electrical signal representative of fluid level in the storage tank. The actuator includes an electromechanical device such as a solenoid that operates the flow disturber via a mechanical linkage in response to the electrical signal.
The present invention and its advantages over the prior art will be more readily understood upon reading the following detailed description and the appended claims with reference to the accompanying drawings.